JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="row flexbox">
    <div class="col-xs-12 col-sm-6 first">

    </div>
    <div class="col-xs-12 col-sm-6 second">

    </div>
  </div>
</div>

CSS

.flexbox {
    display: -webkit-flex;
    -webkit-flex-flow: row; // Children elements will be in rows
    -webkit-flex-wrap: wrap;
    width: 100%;
}
.first
{
    border:1px solid red;    
    height:50px;
    width:200px;
}
.second{
    border:1px solid green;
    width:100%;  
    -webkit-flex: 1;
    height:80px;
}
@media (max-width: 767px) {    
    .flexbox {    
        -webkit-flex-flow: column;    
    }
    .first,.second{
        width:100%;
    }    
    
}

JavaScript

2